Fuse with retractable indicator strip

ABSTRACT

A fuse for monitoring low level electrical energy by means of a strip of resilient material disposed beneath a translucent surface, with one end supported by a portion of a terminal pin inside an enclosure, and the other end supported by a wire to another terminal pin. The strip is formed to have residual stresses, such that when electrical energy at a predetermined level disintegrates the wire, the strip retracts. The width of the strip is such that the retracted position is easily detected as contrasted with the extended position. To improve visibility during the night, and often during the day, a light source is used in one embodiment of the invention such that retraction of the strip is detected more easily.

United States atent Williams 1 May 23, 1972 [54] FUSE WITH RETRACTABLEINDICATOR STRW [72] inventor:

' Fort Worth, Tex. 761 I6 221 Filed: Aug. 28, 1970 [21] Appl.No.: 67,892

[56] References Cited UNITED STATES PATENTS 3,340,430 9/ l 967 Jenkins..337/206 2,204,948 6/1 940 Pond ...337/265 2,036,008 3/ l 936 White..337/266 Robert A. Williams, 55 Bounty Road East,

" 238mm Examiner-F. E. Bell Attomey wofiord, Felsman and Fails [57]ABSTRACT A fuse for monitoring low level electrical energy by means of astrip of resilient material disposed beneath a translucent surface, withone end supported by a portion of a terminal pin inside an enclosure,and the other end supported by a wire to another tenninal pin. The stripis formed to have residual stresses, such that when electrical energy ata predetermined level disintegrates the wire, the strip retracts. Thewidth of the strip is such that the retracted position is easilydetected as contrasted with the extended position. To improve visibilityduring the night, and often during the day, a light source is used inone embodiment of the invention such that retraction of the strip isdetected more easily.

10 Claims, 10 DrawingFigures Patented May 23, 1972 3,665,361

2 Sheets-Sheet 1 INVENTOR Patented May 23, 1972 3,665,361

2 Sheet s-Sheet 2 lNl/E/V TOR l ATTORNEYS I, V- a? m FUSE WITHRETRACTABLE INDICATOR STRIP BACKGROUND OF THE INVENTION 1 1. Field ofthe Invention:

This invention relates in general to fuse apparatus or electrical energymonitors for the detection of excessive levels of electrical energy, andin particular to apparatus that is operational at extremely low energylevels, yet easily detected.

2. Description of the Prior Art There are a wide variety of fusedevicesin the prior an addressed to the problem of how best to detectthe disintegration ofa fusible element that may be extremelysmall. US.Pat. No. 1,520,201 illustrates one such device in which the melting ofthe fusible element causes a. platemounted on a flexible shaft to pivotfrom an invisible to a visible position. US. Pat. No. l,56'-7,529'illustrates a fuse device in which the melting of the fusible elementenables a spring mounted plate to move from aninvisible to avisiblepositiom- SUMMARY OFTHEINVENTION The invention is a means formonitoring low level electrical energy through. the provision of aneasily detected visual means for determining, in lightness or darkness,whether a associated electrical circuit. This monitoring device wasdeveloped for weapons systems whereaccurate detection of possiblyextremely low levels of electrical energy is essential.

In U.S. Pat. No. 3,505,635 I disclose a pyrotechnic detonator circuittest probe that issuccessfully utilized to prevent premature ejection ofarming devicessuch as bombs or missiles from aircraft. Commonly, suchunwanted ejections are caused by the presence of stray electrical energythat is present in the detonator circuit when arming an aircraft. In aco-pending application entitled "Electrical Contact Test .Ap paratus"Ser. No. l8,97l,' filed Mar. l2, 1970, I disclosed test apparatusespecially suitable for testing the breach or. breach cap used withejection racksin military aircraft. In this test apparatus'there is needfor an indicator for spurious electrical energy. The present inventionis 'ideally adapted to serve as such an indicator.

Broadly, the invention includes an enclosure means with a translucenttop, with twoterminal pins insulated from each other and-extendingthrough a portion of the enclosure. A resilient and retractable strip,which in its relaxed position assumes a curved, retractedconfiguration,has one end secured to one terminal pin, while the other end is heldinan extended position by means of an electrically conducted wire securedto result, including a coating of radium on a lower portion of .the

enclosure'beneath the electrically conductive strip. Other details andadvantages of the invention will become apparent in the followingdetailed description.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side elevation view,partially in longitudinal section, showing an electrical energy monitorconstructed in accordance with the principles of the invention;

FIG. 2.is a plan view of the apparatus of FIG. 1;

FIG. 3 is a sidev elevation view, partially in longitudinal section,showing a modified form of electrical energy monitor;

FIG. 4 is a plan view of the apparatus shown in FIG. 3;

FIG. 5 is a side elevation view, partially in longitudinal section,showing an alternate form of electrical energy monitor, and one form oflight source used in combination therewith;

predetermined level of electrical energy was exceeded in the FIG. 6 is aplan view of yet another form of electrical energy monitor constructedin accordance with the principles of the invention; V

FIG. 7 is a side elevation view, partially in section, of the apparatusshown in FIG. 6; and

FIG. 8 is a side elevation view of one of the terminal pins of theapparatus shown in FIGS. 3 through 7.

FIG. 9 is a front elevation view of the other of the terminal pins ofFIGS. 3 through 7.

FIG. 10 is a side elevation view, partially in longitudinal section,showing an alternate form of electrical energy monitor, identical to theFIG. 5 embodiment, except for the use of an alternate light source.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The numeral 11 in the drawingdesignates an enclosure means having in this instance, a translucent top13 supported by side walls l5'having a cylindrical wall section and aninwardly, radially extending shoulder 17. A lower outwardly, radiallyextending shoulder 19 is secured to a base portion 21 through whichextends two terminalpins 23,25 that have inner end portions 27, 29protruding into an interior cavity 31 inside the enclosure means.

The terminal pins 23, 25 are insulated from each other, from theenclosure, and from the base portion 21 thereof by rings of electricallynon-conductive material 33, 35, leaving a pair of outer end portions 37,39 that protrude from the exterior of the enclosure means for insertioninto socket means (not shown) of an electrical circuit to be monitored.

An electrically conductive and resilient strip 41 has one end region 43welded or attached to the inner end portion 27 of the terminal 23, withthe other end portion 45 being secured to the inner end portion 29 ofthe terminal 25 by a thin, electrically conductive and fusible wire 47that is secured to the strip 41 and terminal 29 by welding or othersuitable means. As shown in FIG. 1, the resilient strip 41 is thus heldin an extended configuration, and is residually stressed such that whenthe wire 47is melted by excessive electrical energy, the strip assumes aretracted configuration, as shown in phantom in FIG. 1. Such retractionis easily detected from a view above the translucent top 13.

For the purpose of improving the visibility of the monitor at night, asmall metal plate 48 having a radium coating 49 on its exterior issecured between the terminal pins on an inner surface of the baseportion 21 of the enclosure means 11, with the resilient strip in itsextended position being between the light source and the translucent topsuchthat in the retracted position, the resilient strip exposes theradium light source;

By way of example only, and not limitation, the translucent top 13 maybe fabricated of glass, and the side walls 15 and base portion 21 may beconstructed of Kovar metal. The glass, translucent top 13 and side wall15 may be connected by being brazed in the Kovar metal, and the sidewall connected with the base portion 21 by welding. The terminal pins23, 25 are preferably constructed of Kovar that is gold plated, withinsulation rings 33, 35 being constructed of glass.

The resilient strip 41 may be constructed of nickel having a relaxedconfiguration as shown in phantom in FIG. 1 and a thickness in a rangeof from 0.0002 to 0.002 inches and a width of 0.125 inches. The wire 47is preferably constructed of tungsten or aluminum having a thickness ina range from 0.0001 to 0.005 inches, preferably 0.0002 inch. Currents aslow as 0.01 millijoules may be detected with the smallest of the abovedimensions.

In operation, the terminal pins 25, 27 and their outer end portions 37,39 are inserted into receiving sockets (not shown) of an electricalcircuit whose energy is to be monitored. When the circuit is energized,electrons flow between terminal pins 23, 25 through the resilient strip41 and the connecting, electrically conductive wire 47. Should theelectrical energy exceed the capacity of the fusible wire element 47,this element will have its metallurgical characteristics sufficientlyaltered by heat to fracture, thus enabling the residual stresses in thestrip 41 to cause it to assume the retracted configuration shown inphantom in FIG. 1. During the daytime, the retraction of this strip canbe easily detected, and at night, the detection simplified through useof the light source 49, which in this instanceis a radium light source,but which could be an incandescent light, flourescent light, orBetalight," which is a glass capsule, internally coated with a phospherand filled with tritium gas, the radioactive isotope of hydrogen, whichon decay emits exclusively Beta particles, i.e., electrons, with amaximum energy of 18.6 Kev. The Beta particles resulting from theradioactive decay are absorbed by the phospher, causing it to emit lightcontinuously in the visible spectrum. The glass is impervious to tritiumand completely absorbs any Beta radiation not already absorbed in thephospher. Such lights are explained in detail, with specifications, inthe Standard Betalight Handbook, available from Canrad PrecisionIndustries, Inc. of 630 Fifth Avenue, New York, New York.

In FIGS. 3 and 4 is illustrated an alternate embodiment of the inventionin which an hermetically sealed glass enclosure 51 is fused aroundterminal pins 53, 55, as shown in FIG. 3. Terminal pin 53 supportsthrough a slot 57 an electrically conductive resilient strip 59 havingits outermost end portion 61 curved downward and supported by a wire 63inserted into a receiving aperture 65 in the terminal pin 55 as shown inFIG. 10. As in the embodiment shown in FIG. 1 and 2, strip 59 and wire63 are secured to their respective terminal pins by suitable soldermaterial.

FIG. shows another embodiment of the invention in which a glassenclosure 65 is formed around two terminal pins 67, 69 that support aresilient strip of material 71 and a fusible wire 73 in the same manneras the embodiment shown in FIGS. 3 and 4. The lower end portions 75, 77are inserted in receiving sockets 79, 81 connected with electricalconductors 83,85 leading to terminals 87, 89 connected with an electricpower source 91 disposed on either side of the base 93 that supportedthe glass enclosure 65. Sockets designated respectively 95, 97 are alsosupported by base 93 and receive in this instance incandescent bulbs 99,101. Socket 95 is connected between electrical conductors 103, 105 thatin turn are connected across the power source 91 in a manner similar tothe connection of electrical conductors, 107, 109 leading to the socket97. Hence, the incandescent bulbs 99, 101, provide a light source tobetter illuminate the monitoring device to improve visibility ofresilient strip 71 to better indicate its retracted position.

Another embodiment is illustrated in FIGS. 6 and 7 in which the terminalpost 111, 113 supports a fusible form of electrically conductive wire115, over which a curved end portion 117 of a strip or resilientmaterial 119, which may be, but is not necessarily electricallyconductive, is placed, such strip extending through a slot 121 in asupport post 123. In operation and when the monitored electric energyexceeds a predetermined level, the wire 115 fractures, enabling theresilient strip 119 to assume a retracted position that is easilyvisible.

In FIG. is shown an embodiment similar to that of FIG. 5, having theglass enclosure 65 around tenninal pins 67, 69 that support a resilientstrip of material 71 and a fusible wire 73. Moreover, the lower endportions 75, 77 are inserted within the receiving sockets 79, 81connected with electrical conductors 83, 85 of a circuit to bemonitored. A light source 120, which is a tritium gas filled glasscapsule of the type previously described is secured by a suitableadhesive within the annular groove 122. Such a combination isadvantageous in that no external source of energy is required for thelight source and as compared to the FIG. 1 embodiment, no radioactivematerials are carried by the glass enclosure 65 of the fuse per se.

It should be apparent from the foregoing description that apparatushaving significant advantages has been provided. The use of a ship ofresilient material stretched between two terminal pins in its extendedconfiguration and maintained in that configuration by a thin,electrically conductive wire secured to the strip and at leastoneterrninal pin, enables the sensing of circuit overloads when workingwith very small quantities of electrical energy. The electricallyconductive wire may be quite small in diameter such that it will fuse ordisintegrate at the low energy levels that frequently must be detectedin circuits such as those associated with the previously describeddetonator circuits used in weapons systems, especially those in modern,military aircraft. Although only a predetermined, low level electricalenergy may be used to destroy the wire, the width of the'resilientstrip, which assumes a retracted position in the embodiment shown,through the use of residual stresses, enables convenient and rapiddetection of the presence of excessive electrical energy. In addition,the use of a light source in combination with the above describedretractable strip enables detection at night, and easier detectionduring the daytime, an especially advantageous feature of the inventionwhen considering its use in military aircraft weapon systems, which mustbe armed under adverse lighting conditions, frequently at night.

While the invention has been shown in only a few of its forms, it shouldbe apparent to those skilled in the art that it is not so limited but issusceptible to various changes and modifications without departing fromthe spirit thereof.

I claim:

- 1. An electrical energy monitor especially adapted to detect electricenergy levels below a predetermined, low level, said monitor comprising:I

enclosure means having at least a translucent top; two terminal pinsinsulated from each other and extending through a portion of theenclosure means to define a pair of outer end portions that protrudeexteriorly from the enclosure means and a pair of inner end portionsprotruding into an interior cavity;

an electrically conductive, resilient strip, having an easily visiblewidth greater than its thickness and which in its relaxed positionassumes a curved, retracted configuration, one end region of the stripbeing secured to the inner end portion of one of the terminal pins;

an electrically conductive wire secured tothe other end region of theelectrically conductive strip and carried by the inner end portion ofthe other of said terminal pins to stretch said strip to an extendedconfiguration to generate residual, ilexural stresses therein.

2. The monitor defined by claim 1 in which the said resilient strip hasa thickness in a range from 0.0002 to 0.002 inches.

3. The monitor defined by claim 2 in which said wire has thickness in arange from 0.0001 to 0.005 inches.

4. The monitor defined by claim 1 which further includes a light sourcecarried by the enclosure means generally between the terminal pins, withsaid resilient strip in its extended configuration being between thelight source and the translucent top of the enclosure means.

5. An electrical energy monitor especially adapted to detect electricenergy levels below a predetermined, low level, said monitor comprising:

enclosure means having at least a translucent top;

two terminal pins insulated from each other and extending through aportion of the enclosure means to define a pair of outer end portionsthat protrude exteriorly from the enclosure means and a pair of innerend portions protruding into an interior cavity;

a retractable strip having an easily visible width greater than 7 itsthickness and which in its relaxed position assumes a curved, retractedconfiguration, one end region of the strip being secured to the innerend portion of one of the terminal pins;

an electrically conductive wire secured to said strip and communicatingelectrically between said terminal pins, maintaining said strip in anextended position.

6. The monitor defined by claim 5 which further includes a light sourcecarried adjacent the enclosure means with said resilient strip in itsextended configuration being exposed to the light source.

7. An electrical energy monitor especially adapted to detect electricenergy levels below a predetermined, low level, said monitor comprising:

enclosure means having at least a translucent top;

two terminal pins insulated from each other and extending 5 saidresilient strip being held by said wire to an extended residuallystressed configuration. 8. The monitor defined by claim 7 in which thesaid resilient strip has a thickness in a range from 0.0002 to 0.002inches.

9. The monitor defined by claim 8 in which said wire has a thickness ina range from 0.0001 to 0.005 inches.

10. The monitor defined by claim 7 which further comprises:

support means located in said enclosure for supporting one end of saidresilient strip; said wire extending between and being supported by bothof said terminal pins; the other end of said resilient strip beingsupported by said wire extending between said terminal pins.

* k H l I.

1. An electrical energy monitor especially adapted to detect electricenergy levels below a predetermined, low level, said monitor comprising:enclosure means having at least a translucent top; two terminal pinsinsulated from each other and extending through a portion of theenclosure means to define a pair of outer end portions that protrudeexteriorly from the enclosure means and a pair of inner end portionsprotruding into an interior cavity; an electrically conductive,resilient strip, having an easily visible width greater than itsthickness and which in its relaxed position assumes a curved, retractedconfiguration, one end region of the strip being secured to the innerend portion of one of the terminal pins; an electrically conductive wiresecured to the other end region of the elecTrically conductive strip andcarried by the inner end portion of the other of said terminal pins tostretch said strip to an extended configuration to generate residual,flexural stresses therein.
 2. The monitor defined by claim 1 in whichthe said resilient strip has a thickness in a range from 0.0002 to 0.002inches.
 3. The monitor defined by claim 2 in which said wire has athickness in a range from 0.0001 to 0.005 inches.
 4. The monitor definedby claim 1 which further includes a light source carried by theenclosure means generally between the terminal pins, with said resilientstrip in its extended configuration being between the light source andthe translucent top of the enclosure means.
 5. An electrical energymonitor especially adapted to detect electric energy levels below apredetermined, low level, said monitor comprising: enclosure meanshaving at least a translucent top; two terminal pins insulated from eachother and extending through a portion of the enclosure means to define apair of outer end portions that protrude exteriorly from the enclosuremeans and a pair of inner end portions protruding into an interiorcavity; a retractable strip having an easily visible width greater thanits thickness and which in its relaxed position assumes a curved,retracted configuration, one end region of the strip being secured tothe inner end portion of one of the terminal pins; an electricallyconductive wire secured to said strip and communicating electricallybetween said terminal pins, maintaining said strip in an extendedposition.
 6. The monitor defined by claim 5 which further includes alight source carried adjacent the enclosure means with said resilientstrip in its extended configuration being exposed to the light source.7. An electrical energy monitor especially adapted to detect electricenergy levels below a predetermined, low level, said monitor comprising:enclosure means having at least a translucent top; two terminal pinsinsulated from each other and extending through a portion of theenclosure means to define a pair of outer end portions that protrudeexteriorly from the enclosure means and a pair of inner end portionsprotruding into an interior cavity; a resilient strip located in saidenclosure means and having an easily visible width greater than itsthickness and which in its relaxed position assumes a curved, retractedconfiguration; an electrically conductive wire located in said enclosuremeans and in electrical communication with said terminal pins; saidresilient strip being held by said wire to an extended residuallystressed configuration.
 8. The monitor defined by claim 7 in which thesaid resilient strip has a thickness in a range from 0.0002 to 0.002inches.
 9. The monitor defined by claim 8 in which said wire has athickness in a range from 0.0001 to 0.005 inches.
 10. The monitordefined by claim 7 which further comprises: support means located insaid enclosure for supporting one end of said resilient strip; said wireextending between and being supported by both of said terminal pins; theother end of said resilient strip being supported by said wire extendingbetween said terminal pins.